1. Field of the Invention
The present invention generally relates to a shock wave generating apparatus capable of disintegrating an object within a biological object under medical examination, e.g., a cancer cell, and a concretion by utilizing focused energy of shock waves. More specifically, the present invention is directed to a shock wave generating apparatus capable of generating a wide concretion-disintegrating region by the focused shock waves.
2. Description of the Related Art
Various types of shock wave generating apparatuses have been proposed in, for instance, Japanese KOKAI (Disclosure) patent application No. 62-49843 (1987). In FIG. 1, there is shown, as a sectional view, an ultrasonic wave applicator of one conventional shock wave generating apparatus.
The construction of this ultrasonic wave application is as follows. A through hole having a predetermined shape is formed in a center portion of this applicator 1. A vibrating element (e.g., piezoelectric transducer element) 2 is spherically formed and a backing material 3 is uniformly adhered to a rear surface of this spherical vibrating element 2. An imaging ultrasonic probe 4 is positioned in such a manner that a transmitting/receiving wave front (ultrasonic array) 4a is located at the curved surface identical to the shock wave transmitting/receiving wave front of the vibrating element 2, or backward the last-mentioned wave front. Furthermore, this ultrasonic wave applicator 1 includes a water bag 5 containing water as a coupling medium for the ultrasonic wave. Reference numeral 6 indicates a biological body under medical examination.
To disintegrate a concretion or calculus within a biological body by utilizing the above-described conventional shock wave generating apparatus, the focal point of the generated shock wave must be pointed to this concretion, which will be referred to as "a positioning of a focal point". Such a positioning of a focal point is performed under the condition that while both a B-mode image (tomographic image) of the biological body and a marker indicative of the focal point are displayed on the display means, this focal point marker is tried to be coincident with the concretion displayed on the display screen. This conventional focal point positioning is described in, for instance, U.S. Pat. No. 4,617,931 to J. Dory entitled "ULTRASONIC PULSE APPARATUS FOR DESTROYING CALCULUSES" issued on Oct. 21, 1986. It should be noted that the marker indicates the focal point defined by the geometrical parameters of the vibrating element 2.
FIGS. 2A to 2C illustrate relationships between the shock wave front and focused region in the conventional shock wave generating apparatus shown in FIG. 1.
In FIG. 2A, reference numeral 7 indicates a single focused region of the shock wave transmitted from the vibrating element 2. This vibrating element 2 is subdivided into six portions as illustrated in FIG. 2B, and the six portions are arranged in a spherical form as represented in FIG. 2A. It should be noted that only one focused region 7 is formed from six element portions "a" to "f". FIG. 2C is an illustration of the focused region 7 as viewed from the transmission direction of the shock wave toward an object 8 to be disintegrated.
Assuming now that an area indicative of a half value of a peak pressure produced by a shock wave transmitted from a vibrating element is defined as the above-described focused region 7, this focused region 7 is geometrically determined by the diameter of the spherical body and the aperture of the vibrating element 2. As apparent from FIG. 2C, since a size of this focused region 7 is very small as compared with the object 8 to be disintegrated within the biological body, the calculus disintegrating efficiency by the shock wave is considerably lowered, which necessarily requires a large quantity of time so as to completely disintegrate the object 8.
The present invention has been made in an attempt to solve the above-described problems of the conventional shock wave generating apparatus, and therefore, has an object to provide a shock wave generating apparatus capable of improving the concretion disintegrating efficiency with respect to the object to be disintegrated within the biological body.